Improved Differentiation of Streptococcus pneumoniae and Other S. mitis Group Streptococci by MALDI Biotyper Using an Improved MALDI Biotyper Database Content and a Novel Result Interpretation Algorithm.

Reliable distinction of and viridans group streptococci is important because of the different pathogenic properties of these organisms. Differentiation between and closely related species group streptococci has always been challenging, even when using such modern methods as 16S rRNA gene sequencing or matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. In this study, a novel algorithm combined with an enhanced database was evaluated for differentiation between and species group streptococci. One hundred one clinical species group streptococcal strains and 188 clinical strains were identified by both the standard MALDI Biotyper database alone and that combined with a novel algorithm. The database update from 4,613 strains to 5,627 strains drastically improved the differentiation of and species group streptococci: when the new database version containing 5,627 strains was used, only one of the 101 species group isolates was misidentified as , whereas 66 of them were misidentified as when the earlier 4,613-strain MALDI Biotyper database version was used. The updated MALDI Biotyper database combined with the novel algorithm showed even better performance, producing no misidentifications of the species group strains as All strains were correctly identified as with both the standard MALDI Biotyper database and the standard MALDI Biotyper database combined with the novel algorithm. This new algorithm thus enables reliable differentiation between pneumococci and other species group streptococci with the MALDI Biotyper.